#![allow(dead_code)] // REMOVE THIS LINE after fully implementing this functionality

use std::collections::HashMap;
use std::ops::Bound;
use std::path::{Path, PathBuf};
use std::sync::atomic::AtomicUsize;
use std::sync::Arc;

use anyhow::Result;
use bytes::Bytes;
use parking_lot::{Mutex, MutexGuard, RwLock};

use crate::block::Block;
use crate::compact::{
    CompactionController, CompactionOptions, LeveledCompactionController, LeveledCompactionOptions,
    SimpleLeveledCompactionController, SimpleLeveledCompactionOptions, TieredCompactionController,
};
use crate::lsm_iterator::{FusedIterator, LsmIterator};
use crate::manifest::Manifest;
use crate::mem_table::MemTable;
use crate::table::SsTable;

pub type BlockCache = moka::sync::Cache<(usize, usize), Arc<Block>>;

/// Represents the state of the storage engine.
#[derive(Clone)]
pub struct LsmStorageState {
    /// The current memtable.
    pub memtable: Arc<MemTable>,
    /// Immutable memtables, from latest to earliest.
    pub imm_memtables: Vec<Arc<MemTable>>,
    /// L0 SSTs, from latest to earliest.
    pub l0_sstables: Vec<usize>,
    /// SsTables sorted by key range; L1 - L_max for leveled compaction, or tiers for tiered
    /// compaction.
    pub levels: Vec<(usize, Vec<usize>)>,
    /// SST objects.
    pub sstables: HashMap<usize, Arc<SsTable>>,
}

impl LsmStorageState {
    fn create(options: &LsmStorageOptions) -> Self {
        let levels = match &options.compaction_options {
            CompactionOptions::Leveled(LeveledCompactionOptions { max_levels, .. })
            | CompactionOptions::Simple(SimpleLeveledCompactionOptions { max_levels, .. }) => (1
                ..=*max_levels)
                .map(|level| (level, Vec::new()))
                .collect::<Vec<_>>(),
            CompactionOptions::Tiered(_) | CompactionOptions::NoCompaction => Vec::new(),
        };
        Self {
            memtable: Arc::new(MemTable::create(0)),
            imm_memtables: Vec::new(),
            l0_sstables: Vec::new(),
            levels,
            sstables: Default::default(),
        }
    }
}

pub struct LsmStorageOptions {
    // Block size in bytes
    pub block_size: usize,
    // SST size in bytes, also the approximate memtable capacity limit
    pub target_sst_size: usize,
    // Maximum number of memtables in memory, flush to L0 when exceeding this limit
    pub num_memtable_limit: usize,
    pub compaction_options: CompactionOptions,
    pub enable_wal: bool,
}

impl LsmStorageOptions {
    pub fn default_for_week1_test() -> Self {
        Self {
            block_size: 4096,
            target_sst_size: 2 << 20,
            compaction_options: CompactionOptions::NoCompaction,
            enable_wal: false,
            num_memtable_limit: 50,
        }
    }

    pub fn default_for_week1_day6_test() -> Self {
        Self {
            block_size: 4096,
            target_sst_size: 2 << 20,
            compaction_options: CompactionOptions::NoCompaction,
            enable_wal: false,
            num_memtable_limit: 2,
        }
    }
}

/// The storage interface of the LSM tree.
pub(crate) struct LsmStorageInner {
    pub(crate) state: Arc<RwLock<Arc<LsmStorageState>>>,
    pub(crate) state_lock: Mutex<()>,
    path: PathBuf,
    pub(crate) block_cache: Arc<BlockCache>,
    next_sst_id: AtomicUsize,
    pub(crate) options: Arc<LsmStorageOptions>,
    pub(crate) compaction_controller: CompactionController,
    pub(crate) manifest: Option<Manifest>,
}

/// A thin wrapper for `LsmStorageInner` and the user interface for MiniLSM.
pub struct MiniLsm {
    pub(crate) inner: Arc<LsmStorageInner>,
    /// Notifies the L0 flush thread to stop working. (In week 1 day 6)
    flush_notifier: crossbeam_channel::Sender<()>,
    /// The handle for the compaction thread. (In week 1 day 6)
    flush_thread: Mutex<Option<std::thread::JoinHandle<()>>>,
    /// Notifies the compaction thread to stop working. (In week 2)
    compaction_notifier: crossbeam_channel::Sender<()>,
    /// The handle for the compaction thread. (In week 2)
    compaction_thread: Mutex<Option<std::thread::JoinHandle<()>>>,
}

impl Drop for MiniLsm {
    fn drop(&mut self) {
        self.compaction_notifier.send(()).ok();
        self.flush_notifier.send(()).ok();
    }
}

impl MiniLsm {
    pub fn close(&self) -> Result<()> {
        unimplemented!()
    }

    /// Start the storage engine by either loading an existing directory or creating a new one if the directory does
    /// not exist.
    pub fn open(path: impl AsRef<Path>, options: LsmStorageOptions) -> Result<Arc<Self>> {
        let inner = Arc::new(LsmStorageInner::open(path, options)?);
        let (tx1, rx) = crossbeam_channel::unbounded();
        let compaction_thread = inner.spawn_compaction_thread(rx)?;
        let (tx2, rx) = crossbeam_channel::unbounded();
        let flush_thread = inner.spawn_flush_thread(rx)?;
        Ok(Arc::new(Self {
            inner,
            flush_notifier: tx2,
            flush_thread: Mutex::new(flush_thread),
            compaction_notifier: tx1,
            compaction_thread: Mutex::new(compaction_thread),
        }))
    }

    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
        self.inner.get(key)
    }

    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
        self.inner.put(key, value)
    }

    pub fn delete(&self, key: &[u8]) -> Result<()> {
        self.inner.delete(key)
    }

    pub fn scan(
        &self,
        lower: Bound<&[u8]>,
        upper: Bound<&[u8]>,
    ) -> Result<FusedIterator<LsmIterator>> {
        self.inner.scan(lower, upper)
    }

    pub fn force_flush(&self) -> Result<()> {
        self.inner
            .force_freeze_memtable(&self.inner.state_lock.lock())?;
        self.inner.force_flush_next_imm_memtable()
    }

    pub fn force_full_compaction(&self) -> Result<()> {
        self.inner.force_full_compaction()
    }
}

impl LsmStorageInner {
    pub(crate) fn next_sst_id(&self) -> usize {
        self.next_sst_id
            .fetch_add(1, std::sync::atomic::Ordering::SeqCst)
    }

    /// Start the storage engine by either loading an existing directory or creating a new one if the directory does
    /// not exist.
    pub(crate) fn open(path: impl AsRef<Path>, options: LsmStorageOptions) -> Result<Self> {
        let path = path.as_ref();
        let state = LsmStorageState::create(&options);

        let compaction_controller = match &options.compaction_options {
            CompactionOptions::Leveled(options) => {
                CompactionController::Leveled(LeveledCompactionController::new(options.clone()))
            }
            CompactionOptions::Tiered(options) => {
                CompactionController::Tiered(TieredCompactionController::new(options.clone()))
            }
            CompactionOptions::Simple(options) => CompactionController::Simple(
                SimpleLeveledCompactionController::new(options.clone()),
            ),
            CompactionOptions::NoCompaction => CompactionController::NoCompaction,
        };

        let storage = Self {
            state: Arc::new(RwLock::new(Arc::new(state))),
            state_lock: Mutex::new(()),
            path: path.to_path_buf(),
            block_cache: Arc::new(BlockCache::new(1024)),
            next_sst_id: AtomicUsize::new(1),
            compaction_controller,
            manifest: None,
            options: options.into(),
        };

        Ok(storage)
    }

    /// Get a key from the storage. In day 7, this can be further optimized by using a bloom filter.
    pub fn get(&self, _key: &[u8]) -> Result<Option<Bytes>> {
        unimplemented!()
    }

    /// Put a key-value pair into the storage by writing into the current memtable.
    pub fn put(&self, _key: &[u8], _value: &[u8]) -> Result<()> {
        unimplemented!()
    }

    /// Remove a key from the storage by writing an empty value.
    pub fn delete(&self, _key: &[u8]) -> Result<()> {
        unimplemented!()
    }

    pub(crate) fn path_of_sst_static(path: impl AsRef<Path>, id: usize) -> PathBuf {
        path.as_ref().join(format!("{:05}.sst", id))
    }

    pub(crate) fn path_of_sst(&self, id: usize) -> PathBuf {
        Self::path_of_sst_static(&self.path, id)
    }

    pub(crate) fn path_of_wal_static(path: impl AsRef<Path>, id: usize) -> PathBuf {
        path.as_ref().join(format!("{:05}.wal", id))
    }

    pub(crate) fn path_of_wal(&self, id: usize) -> PathBuf {
        Self::path_of_wal_static(&self.path, id)
    }

    fn sync_dir(&self) -> Result<()> {
        unimplemented!()
    }

    /// Force freeze the current memtable to an immutable memtable
    pub fn force_freeze_memtable(&self, _state_lock_observer: &MutexGuard<'_, ()>) -> Result<()> {
        unimplemented!()
    }

    /// Force flush the earliest-created immutable memtable to disk
    pub fn force_flush_next_imm_memtable(&self) -> Result<()> {
        unimplemented!()
    }

    /// Create an iterator over a range of keys.
    pub fn scan(
        &self,
        _lower: Bound<&[u8]>,
        _upper: Bound<&[u8]>,
    ) -> Result<FusedIterator<LsmIterator>> {
        unimplemented!()
    }
}